Rating of Electric Equipment Under Intermittent Load

Resistance welding furnishes a clear-cut case of intermittent load. The more elaborate and expensive equipment that marks the trend in welding away from a blacksmith´s art to a carefully controlled science warrants increased care in design. This paper explores one aspect of this design: the thermal limits to the periodic load that can be carried. In this case the application is to resistance-welding problems, and illustrative material is drawn from a type of interleaved flexible welding cable that has seen seven years´ service in industry. The principles, however, apply to all types of welding: in fact, they extend to many fields in which the problem is to find the reaction to an intermittent force??such as electrical or mechanical transients.